1. Field of the Invention
This invention concerns an aircraft assembly tool and a method of manufacturing such a tool.
2. Discussion of the Prior Art
Aircraft assembly tools are designed to support aircraft components while they are being worked on and to locate different components together in the correct relative positions during aircraft assembly. Traditionally, each different assembly process has required at least one dedicated assembly tool, which is produced specifically for a given set of components and which is designed to support the components in a particular manner so that assembly operations can be carried out without interference from the tool. Such assembly tools have had to be manufactured to exacting standards.
A conventional assembly tool comprises a rigid metal jig whose framework is constructed from welded box section steel. A plurality of pick-up devices is mounted on the framework for carrying the aircraft components during the assembly process, and these too are conventionally produced from welded steel parts.
Each assembly tool has to be specifically designed for the component to be supported, and the requirement in the aircraft industry for an aircraft component to be supported with a very high degree of precision means that every stage of construction of the conventional jig has to be carried out to very exacting levels of accuracy. This makes the production of such jigs time-consuming and costly, and they cannot easily be reconfigured for supporting different components, or repaired/adjusted so as to accommodate wear and tear.
As is evident, such an arrangement has significant drawbacks, not the least of which are the high tooling costs resulting from the requirement for a dedicated jig for each aircraft assembly process together with the levels of accuracy needed for producing each jig. Minor modifications in aircraft component design usually mean that a completely new pick-up device or arrangement thereof must be produced, causing further tooling costs and assembly delays. In addition, wear and tear or damage to a jig generally results in the need for a replacement since repairs and adjustments cannot readily be made whilst maintaining the necessary level of precision and integrity for the framework and the pick-up devices.
In spite of these drawbacks, the construction of such aircraft assembly tooling has remained essentially unchanged for almost fifty years.
There is thus a significant need for an aircraft assembly tooling system that is more flexible in design and more economic to produce and use.
The present invention seeks to provide an assembly tool, and a method of producing such a tool, which is more versatile than conventional arrangements and in which the need for precision is confined to some parts only of the tool and its production.
According to one aspect of the invention an aircraft assembly tool for supporting an aircraft component comprising:
a) a fixture frame configured to provide support at predetermined locations of the frame associated with a plurality of predetermined positions and orientations in space at which the component is to be supported;
b) the fixture frame comprising elongate members having predetermined lengths connected together by means of releasable fastening means;
c) a plurality of pick-up devices, each having a receiving element for carrying the component and comprising further elongate members having predetermined lengths connected together by means of clamping elements adapted selectively to allow at least three degrees of freedom of movement of each receiving element along at least two orthogonal axes and around at least one axis coplanar with the orthogonal axes;
d) the pick-up devices being mounted to the fixture frame at the predetermined locations; and
e) each receiving element being aligned about/around the orthogonal axes with a respective predetermined position and orientation.
The fixture frame may be constructed from lengths of extruded aluminium section with the fastening means securing the lengths together. For example, the extruded aluminium section may be formed with longitudinal channels having lips along their edges, and the fastening means may comprise threaded connecting elements receivable in a channel of one section and threaded receiving means provided by or receivable within a channel of another section.
For reasons of constructional accuracy and for strength and rigidity of the fixture frame, it is preferable that the elongate members are rectangular in cross-section, or have at least one substantially flat, planar surface to which the pick-up devices can be clamped, and moved along if necessaryxe2x80x94to adapt to a different component, for example. It is also important that these planar surfaces of the elongate members are so configured as to remain undistorted when a pick-up device is mounted thereon, particularly when the device is under load from the weight of the aircraft component. This preferred embodiment has the additional advantage that it facilitates rapid movement and/or re-alignment/re-positioning of the pick-up devices. In this embodiment, because in use the pick-up device moves along a planar face, the range of movement necessary to accommodate wear and tear or to adapt to a different component may easily and accurately be modelled in the computer as a movement in a single dimension (along the axes of the elongate member, but without any rotation thereabouts) while taking account of the six degrees of freedom of adjustment possible for the receiving element. Where a desired relocation of the pick-up is not feasible, due e.g. to the position of the elongate member and/or the limited range of adjustment of the receiving element, the required re-alignment may be accommodated by removing the pick-up device abd mounting it instead on one the other planar surfaces of the elongate member. Thus the provision of a planar face to the elongate members ensures that simple movement of the pick-up device relative to the elongate member is limited to movement along a single axis, and without any relative rotation: this is a substantial and advantageous difference over the prior art constructions.
The pick-up devices are preferably of universal construction.
According to another aspect of the invention there is provided a universal pick-up device for mounting on a fixture frame to provide an aircraft assembly tool for supporting an aircraft component during the assembly process, the pick-up device comprising a mounting element for mounting the device on the fixture frame, a receiving element for carrying the aircraft component, and a plurality of elongate members having predetermined lengths connected together by means of clamping elements so as to allow at least three degrees of movement of the receiving element along at least two orthogonal axes and around at least one axis coplanar with the orthogonal axes.
In the preferred embodiment of the invention described below, the combination of elongate members and clamping elements are arranged to allow six degrees of freedom of movement of the receiving element along and around three orthogonal axes.
The pick-up devices may also be formed from aluminium.
The aircraft assembly tool and pick-up device according to the present invention offer a number of significant advantages.
In particular, the invention provides a flexible assembly tooling system that is fully adjustable and re-usable. Adjustments and alterations to the assembly tooling can readily be effected, for example in order to accommodate modifications in the design of the aircraft components. Maintenance simply involves replacement of individual frame members and/or pick-up devices in the event of excessive wear, or repositioning of frame members and/or pick-up devices if relative movement has occurred over time. Furthermore, existing assembly tools can be altered to suit different aircraft components once a particular assembly operation is complete.
Another aspect of the present invention is the method of producing the aircraft assembly tool.
According to this aspect of the invention, a method of producing an aircraft assembly tool for supporting an aircraft component comprising:
a) determining a plurality of predetermined positions and orientations in space at which the component should be supported;
b) designing a fixture frame configured to provide support at predetermined locations of the frame associated with said predetermined positions;
c) constructing the fixture frame by selecting elongate members having predetermined lengths and connecting the elongate members together by means of releasable fastening means;
d) constructing a plurality of pick-up devices, each having a receiving element for carrying the component, by selecting further elongate members having predetermined lengths and connecting the further elongate members together by means of clamping elements adapted selectively to allow at least three degrees of freedom of movement of each receiving element along at least two orthogonal axes and around at least one axis coplanar with the orthogonal axes;
e) mounting the pick-up devices to the fixture frame at the predetermined locations; and
f) moving each receiving element along/around the orthogonal axes to align the receiving element with a respective predetermined position and orientation.
Preferably, step f) comprises setting a receiving element approximately in its predetermined position and orientation, and iterating the steps of measuring the actual position and orientation of the receiving element and moving it towards the predetermined position and orientation until it achieves the predetermined position and orientation.
Preferably, the predetermined positions and orientations for the receiving elements of the pick-up devices are determined from computer aided design data for each aircraft component.
Preferably, the actual position and orientation of each receiving element is measured by a laser tracking device.
The present method and assembly tool, whilst specifically designed for use in the aircraft industry, may also advantageously have application in other fields, for example in the automotive industry.